High carbon spent pot lining and methods of fueling a furnace with the same

ABSTRACT

A method of creating and using a high-carbon spent pot lining (SPL) as a fuel, including delining the high-carbon spent pot lining from an electrolytic cell and combusting the SPL in a furnace.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 61/681,199, filed on Aug. 9, 2012, and U.S. Provisional Application No. 61/788,617, filed on Mar. 15, 2013. The disclosure of U.S. Provisional Applications Nos. 61/681,199 and 61/788,617 are hereby incorporated by reference in their entirety for all purposes.

COPYRIGHT NOTIFICATION

This application includes material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office files or records, but otherwise reserves all copyright rights whatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high-carbon spent pot lining. More particularly, the present invention relates to methods of obtaining and using a high-carbon spent pot lining (“SPL”) as a fuel source.

2. Description of the Related Art

Electrolysis of alumina within an electrolytic cell is the major industrial process for the production of aluminum metal. In an electrolytic cell, an electrical current passed between an anode and a cathode within a bath of molten cryolite containing dissolved alumina. The electrical current causes the deposition of aluminum metal on the cathode. Often, the electrolytic cell is configured as a large tank or cell with carbon or graphite lining materials to contain the molten electrolytic bath (also called the “pot lining”). When the cathode is also made of carbon or graphite materials, portions of the lining may also serve as part of the cathode system. Most aluminum electrolytic cells employ carbon blocks as the pot lining and/or cathode. In addition, the electrolytic cell may include insulation materials, such as refractory brick lining, and a metal shell to define and/or thermally insulate the electrolytic cell.

During operation of the electrolytic cell, contaminants from the molten electrolytic bath and/or metal oxides associated with the electrolytic reaction migrate into the pot lining. Once the pot lining has reached the end of its life span it is removed from the electrolytic cell for disposal. Recycling and/or reuse of the spent pot lining (“SPL”) is complicated because it includes both the original pot lining material (such as carbon or graphite) and contaminants from the molten electrolytic bath, such as metal oxides, cyanide, sodium containing materials, and fluoride compounds subject to environmental use restrictions. In addition, because of the contamination, the carbon content of the SPL may be reduced. In some examples, the carbon content of an SPL may be reduced to less than 50% carbon hindering its use as a fuel source.

SUMMARY OF THE INVENTION

The present invention relates to a high-carbon spent pot lining (“SPL”), and more particularly, to methods of obtaining and using a high-carbon SPL as a fuel source.

Additional goals and advantages of the present invention will become more evident in the description of the figures, the detailed description of the invention, and the claims. The foregoing and/or other aspects and utilities of the present invention may be achieved by providing a method of creating a high-carbon spent pot lining (SPL) fuel, including delining a spent pot lining from an electrolytic cell, and pulverizing the spent pot lining to create a spent pot lining fuel, wherein the spent pot lining comprises at least 65% by weight carbon compounds content, based on a total weight of the spent pot lining, with the remainder comprising one or more of oxygen compounds, cyanide compounds, fluoride compounds, sodium compounds, aluminum compounds, and silicon compounds.

In another embodiment, the delining of the spent pot lining includes removing a 1^(st) bath layer, removing a metal layer, removing a 2^(nd) bath layer, cleaning a cathode block, breaking the cathode block, removing the cathode block, and removing the side blocks (27), wherein the spent pot lining consists essentially of the cathode block.

In another embodiment, the method of delining of the spent pot lining further includes combining the spent pot lining with an enriching compound to create an enriched SPL having at least 65% carbon content, based on a total weight of the enriched SPL, and wherein pulverizing the spent pot lining to create a spent pot lining fuel includes pulverizing the enriched SPL.

The foregoing and/or other aspects and utilities of the present invention may be achieved by providing a method of using an SPL fuel including feeding a fuel comprising the SPL fuel to a burner, and combusting the fuel in the burner to generate a thermal energy and directing the thermal energy to a furnace.

In another embodiment, the fuel further includes a supplemental fuel, and wherein the SPL fuel comprises between 50% and 80% of the fuel.

In another embodiment, the fuel includes no more than 50% supplemental fuel.

In another embodiment, the SPL fuel is an enriched SPL.

In another embodiment, the method of using the enriched SPL fuel as a furnace fuel includes feeding a fuel comprising the enriched SPL fuel to a burner, and combusting the fuel in the burner to generate a thermal energy and directing the thermal energy to a furnace.

In another embodiment, the fuel further includes a supplemental fuel, and wherein the enriched SPL fuel includes between 50% and 80% of the fuel.

The foregoing and/or other aspects and utilities of the present invention may be achieved by providing a method of using an SPL, wherein the SPL fuel has a particle size of at most 150 μm, and the SPL fuel has trace amounts or less of HAP, the SPL fuel has trace amounts or less of BPC's, the SPL fuel has trace amounts or less of Dioxine, and the SPL fuel has trace amounts or less of Furan.

In another embodiment, the SPL fuel includes at most 5% by weight oxygen compounds content, based on the total weight of the SPL fuel, at most 0.5% by weight cyanide compounds content, based on the total weight of the SPL fuel, at most 10% by weight fluoride compounds content, based on the total weight of the SPL fuel, at most 10% by weight sodium compounds content, based on the total weight of the SPL fuel, at most 5% by weight aluminum compounds content, based on the total weight of the SPL fuel, and at most 5% by weight silicon content, based on the total weight of the SPL fuel.

In another embodiment, the SPL fuel has a heat value of at least 18,400 kJ/Kg.

The foregoing and/or other aspects and utilities of the present invention may be achieved by providing a method of using an enriched SPL fuel as a furnace fuel, wherein the enriching compound includes at least 80% by weight carbon compounds content, based on a total weight of the enriching smelting residue, at most 5% by weight oxygen compounds content, based on the total weight of the enriching smelting residue, at most 0.1% by weight cyanide compounds content, based on the total weight of the enriching smelting residue, at most 5% by weight fluoride compounds content, based on the total weight of the enriching smelting residue, at most 5% by weight sodium compounds content, based on the total weight of the enriching smelting residue, at most 5% by weight aluminum compounds content, based on the total weight of the enriching smelting residue, and at most 1% by weight silicon content, based on the total weight of the enriching smelting residue.

In another embodiment, the enriching compound has a heat value of at least 18,400 kJ/Kg

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the various embodiments, taken in conjunction with the accompanying drawings of which:

FIGS. 1-2 illustrate an exemplary electrolytic cell that can be delined to obtain a high-carbon SPL according to embodiments of the present invention.

FIG. 3 illustrates a method of delining an electrolytic cell to obtain a high-carbon SPL according to an embodiment of the present invention.

FIGS. 4-7 illustrate methods of using a high-carbon SPL as a furnace fuel according embodiments of the present invention.

FIG. 8 illustrates an apparatus configured to use a high-carbon SPL as a fuel according to embodiments of the present invention.

The drawings referenced above are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention. Further, some features may be exaggerated to show details of particular components. These drawings/figures are intended to be explanatory and not restrictive of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the various embodiments of the present invention. The embodiments are described below to provide a more complete understanding of the components, processes and apparatuses of the present invention. Any examples given are intended to be illustrative, and not restrictive. Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “in some embodiments” and “in an embodiment” as used herein do not necessarily refer to the same embodiment(s), though they may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, although they may. As described below, various embodiments of the present invention may be readily combined, without departing from the scope or spirit of the present invention.

As used herein, the term “or” is an inclusive operator, and is equivalent to the term “and/or,” unless the context clearly dictates otherwise. The term “based on” is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of “a,” “an,” and “the” include plural references. The meaning of “in” includes “in” and “on.”

All physical properties that are defined hereinafter are measured at 20° to 25° Celsius unless otherwise specified.

When referring to any numerical range of values herein, such ranges are understood to include each and every number and/or fraction between the stated range minimum and maximum. For example, a range of about 0.5-6% would expressly include all intermediate values of about 0.6%, 0.7%, and 0.9%, all the way up to and including 5.95%, 5.97%, and 5.99%. The same applies to each other numerical property and/or elemental range set forth herein, unless the context clearly dictates otherwise.

As used herein, “enriching” means the act or process of adding a compatible material fuel to a first material or fuel. For example, an SPL fuel may be enriched with another source of carbon fuel, such as carbon containing residues from other compatible smelting processes.

FIGS. 1-2 illustrate an exemplary electrolytic cell for the production of aluminum. As illustrated in FIGS. 1-2, an electrolytic cell (1) may include an anode (not illustrated), a cathode (2), a current collector (4), and a steel shell (7). The steel shell (7) may support a sidewall lining (3) and insulations bricks (5) configured to contain and insulate a molten electrolytic bath (15). In some embodiments, the electrolytic cell (1) further includes an insulation layer (6) between the cathode (2) and the insulations bricks (5). In some embodiments, the insulation layer (6) is composed of alumina. In some aluminum electrolytic cells, the cathode (2) and the sidewall lining (3) include carbon or graphite materials. For example, in some embodiments, the cathode (2) and sidewall lining (3) are made of amorphous, graphitic or graphitized carbon blocks. In some embodiments, the carbon blocks are made of an anthracite aggregate mixed with a coal-tar pitch binder. In some embodiments, a ramming paste (8) may be used to fill the joints between the carbon joints to create a liquid-tight pot lining. In some embodiments, the ramming paste (8) includes an anthracite filler and a coal-tar pitch binder.

An aluminum electrolytic cell pot lining has a typical operational life of about 2 to 6 years. After which, the electrolytic cell is shut down, the pot lining is removed and disposed off, and the electrolytic cell is cleaned and prepared for re-lining. During operation, the electrical current supplied to the electrolytic cell maintains the electrolytic bath in a molten state. However, after shutting down, any remaining aluminum metal and electrolytic bath solidifies.

FIG. 3 illustrates a method of delining an electrolytic cell (1) to obtain a high-carbon SPL according to an embodiment of the present invention.

As illustrated in FIG. 3, in one embodiment, a method of delining an electrolytic cell to obtain a high-carbon SPL (20) includes the following operations; removing a 1^(st) bath layer (21); removing a metal layer (22); removing a 2^(nd) bath layer (23); cleaning a cathode block (24); breaking the cathode block (25); removing the cathode block (26); and removing the side blocks (27).

In one embodiment of the present invention, and with reference to FIGS. 2-3, removing a 1^(st) bath layer in operation (21) includes the physical break up and removal of the solidified electrolytic bath (15). As some non-limiting examples, removing the 1^(st) bath layer in operation (21) may include physically removing (e.g. by jack hammering bath components and/or siphoning the dust generated from removing the bath components) the solidified electrolytic bath (15) from the electrolytic cell (1). For example, in one embodiment, an excavator equipped with a bucket is used to break up and collect large pieces of the solidified electrolytic bath (15).

In some electrolytic cell operations, a residual metal layer (16) may remain in the electrolytic cell (1) after shut-down. In one embodiment of the present invention, removing the metal layer (16) in operation (22) includes removing the solid metal layer (16) from the electrolytic cell (1) after removal of the 1^(st) bath layer in operation (21). Physical means may be used to remove the solid metal layer (16). For example, an excavator equipped with a pneumatic drill may be used to take off and/or break the metal layer (16) and pick it up.

As illustrated in FIG. 2, in some embodiments, a 2^(nd) layer of solidified bath (17) may be present underneath the metal layer (16) after shut down of the electrolytic cell (1). In one embodiment of the present invention, removing the 2^(nd) bath layer (17) in operation (23) includes physical break up and removal of the 2^(nd) solidified electrolytic bath layer (17). As some non-limiting examples, removing the 2^(nd) solidified electrolytic bath layer (17) in operation (23) may include physically removing (e.g. by jack hammering bath components and/or siphoning the dust generated from removing the bath components) the 2^(nd) solidified electrolytic bath layer (17) from the electrolytic cell (1).

In one embodiment of the present invention, and with reference to FIGS. 2-3, cleaning a cathode block in operation (24) includes removal of any remaining solidified electrolytic bath after operations (21-23). For example, in one embodiment, a vacuum is used to siphon dust or small debris generated from removing the solidified electrolytic bath (15), the metal layer (16), and/or the 2^(nd) solidified electrolytic bath layer (17) remaining in the electrolytic cell (1) after operations (21-23).

In another embodiment of the present invention, after cleaning the cathode block in operation (24), the cathode block is removed in operations (25-26). Removal of the cathode block in operations (25-26) may include physically breaking up (e.g. by jack hammering or drilling) and removing the cathode block (2). For example, in one embodiment, excavators equipped with pneumatic drills and/or buckets are used to break up and collect large pieces of the cathode block (2).

In some embodiments, a ramming paste (8) joins the cathode block (2) and the sidewall lining (3). In such cases, the breaking of the cathode block in operation (25) is configured to avoid the ramming paste (8) and the sidewall lining (3). For example, in one embedment, the breaking of the cathode block in operation (25) includes breaking up the cathode block (2) from a center thereof towards the sides in order to avoid touching the joints defined by the ramming paste (8) and/or the sidewall lining (3). In some embodiments, the cathode block (2) removed in operations (25-26) does not include substantial amounts of the ramming paste (8) or the sidewall lining (3).

In some embodiments, the presence of an insulation layer (6) between the cathode (2) and the insulations bricks (5) allows the removal of the cathode block (2) separate from the insulation bricks (5). For example, in one embodiment, the cathode block (2) removed in operations (25-26) does not include substantial amounts of the insulations bricks (5).

In one embodiment of the present invention, the cathode block (2) removed in operations (25-26) is used to create a high-carbon SPL.

In another embodiment of the present invention, after the cathode block (2) is removed in operations (25-26), the remaining ramming paste (8) and/or sidewall lining (3) are broken up and removed from the electrolytic cell (1). Removal of the sidewall lining (3) in operation (27) may include physically breaking up (e.g. by jack hammering or drilling) and removing the sidewall lining (3) and/or ramming paste (8). For example, in one embodiment, excavators equipped with pneumatic drills and/or buckets are used to break up and collect large pieces of the sidewall lining (3) and/or ramming paste (8).

In some embodiments of the invention, the spent pot lining materials obtained in operations (25-26) are segregated from the spent pot lining materials obtained in operation (27). In some embodiments, the spent pot lining materials obtained in operations (25-26) do not include substantial amounts of the ramming paste (8) or the sidewall lining (3). In some embodiments, the spent pot lining materials obtained in operations (25-26) do not include substantial amounts of the solidified electrolytic bath (15), the metal layer (16), the 2^(nd) solidified electrolytic bath layer (17), and/or the insulations bricks (5). In some embodiments, the spent pot lining materials obtained in operations (25-26) consist essentially of portions of the cathode block (2).

As illustrated in FIG. 3, in one embodiment of the present invention a high-carbon SPL is obtained from the delining method (20). In one embodiment, the high-carbon SPL includes the spent pot lining materials obtained in operations (25-26). In another embodiment, the high-carbon SPL includes the cathode block (2) obtained in operations (25-26). In some embodiments, the high-carbon SPL consists essentially of the cathode block (2) obtained in operations (25-26). In other embodiments, the high-carbon SPL does not include substantial amounts of the solidified electrolytic bath (15), the metal layer (16), the 2^(nd) solidified electrolytic bath layer (17), and/or the insulations bricks (5) obtained from the delining method (20).

In one embodiment of the present invention, the high-carbon SPL has a carbon content of at least 50% by weight. In another embodiment, the carbon content of the high-carbon spent pot lining is at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 95%, and at least about 98%.

In another embodiment, the high-carbon SPL includes less than 50% non-carbon compounds. For example, in one embodiment, the high-carbon SPL includes at least 65% carbon content by weigh with the remainder including one or more of oxygen compounds, cyanide compounds, fluoride compounds, sodium compounds, aluminum compounds, and silicon compounds.

In another embodiment, the high-carbon SPL does not contain measurable amounts of, or contains only trace amounts of regulated environmental contaminants affecting the use of carbon as a fuel. For example, in one embodiment, the high-carbon SPL contains only trace amounts of organic air toxins, such as dioxins and furans. In another embodiment, the use of the high-carbon SPL does not produce measurable amounts of, or produces only trace amounts of, hazardous air pollutants (HAP), polychlorinated biphenyls (PCBs), hazardous metal air pollutants (e.g., mercury, arsenic, chromium, nickel), or acid gases (e.g., hydrochloric acid (HCl), hydrogen fluoride).

Table 1 illustrates a composition of two example high-carbon SPLs obtained according to embodiments of the present invention. As illustrated in Table 1, embodiments of a high-carbon SPL contain at least 65% carbon content, and no more than 10% of oxygen compounds, cyanide compounds, fluoride compounds, sodium compounds, aluminum compounds, or silicon compounds.

TABLE 1 High Carbon SPL Composition Embodiment 1 (%) Embodiment 2 (%) Carbon Compounds >65 >75 Oxygen Compounds <5 <5 Cyanide Compounds <0.5 <0.2 Fluoride Compounds <10 <7 Sodium Compounds <10 <7 Aluminum Compounds <5 <3 Silicon Compounds <5 <1

In another embodiment of the invention, the high-carbon SPL is combined with an enriching compound to further increase the carbon content of the resulting enriched high-carbon SPL. For example, in one embodiment of the present disclosure, the high-carbon SPL is combined with other carbon containing materials to create an enriched high-carbon SPL. In one embodiment, the high-carbon SPL is enriched by combining it with compatible smelter residues, such as carbon anode or cathode production byproducts. Table 3 illustrates a composition of compatible enriching compounds that can be used to enrich the high-carbon SPL according to embodiments of the present invention. As illustrated in Table 3, Embodiment 1 represents an exemplary carbon anode fabrication process residue usable as an enriching compound. Embodiment 2 is an exemplary carbon anode cleaning process residue usable as an enriching compound. In one embodiment of the present invention, a high-carbon SPL having at least 50% carbon content by weight is enriched with one or more enriching compounds to create an enriched high-carbon SPL having at least a 75% carbon content by weight. In another embodiment of the present invention, a high-carbon SPL having at least a 75% carbon content by weight is enriched with one or more enriching compounds to create an enriched high-carbon SPL having at least a 80% carbon content by weight.

TABLE 3 Enriching Compound Composition Embodiment 1 (%) Embodiment 2 (%) Carbon Compounds >80 >90 Oxygen Compounds <5 <2 Cyanide Compounds <0.1 <0.1 Fluoride Compounds <5 <5 Sodium Compounds <5 <2 Aluminum Compounds <5 <2 Silicon Compounds <1 <1

FIGS. 4-8 illustrate methods of using a high-carbon SPL as a fuel according embodiments of the present invention.

As illustrated in FIG. 4, a general method of using a high-carbon SPL as a fuel includes injecting a fuel having high-carbon SPL into a burner to produce a thermal energy (e.g. heat and/or flame) in operation (110), and directing the thermal energy to a furnace via the burner in operation (112).

FIG. 5 illustrates a method of heating a furnace using a high-carbon SPL according to another embodiment of the present invention. As illustrated in FIG. 5, a method of heating a furnace with a high-carbon SPL fuel includes injecting a fuel having high-carbon SPL into a burner to produce thermal energy (110); directing the thermal energy to a furnace (e.g. into, onto) via the burner (112); and modifying the high-carbon SPL fuel content of fuel in operation (114), followed by reiterating operations 110 and 112.

FIG. 6 illustrates a method of heating a furnace using a high-carbon SPL according to another embodiment of the present invention. As illustrated in FIG. 3, a method of heating a furnace with a high-carbon SPL fuel includes recovering high-carbon SPL from an electrolytic cell (1) in operation (116), co-feeding the high-carbon SPL fuel and another fuel (e.g. combustible air) into a burner (118), and directing a thermal energy (e.g. heat, flame) from the burner to a furnace (e.g. into/onto the furnace) in operation (120). In some embodiments of the present invention, recovering high-carbon SPL from an electrolytic cell (1) refers to obtaining a high-carbon SPL by delining an electrolytic cell (1) through operations (25-26) described above. In other embodiments, recovering high-carbon SPL from an electrolytic cell (1) includes delining an electrolytic cell (1) to obtain a high-carbon SPL, grinding and/or purifying the high-carbon SPL to a particle size suitable for injection into the burner of operation (118). In one embodiment, after delining the electrolytic cell to obtain the high-carbon SPL, a purifying operation is completed to further remove non-carbon contaminants (e.g. insulating brick, solidified bath, and alumina) prior to grinding the high-carbon SPL.

FIG. 7 illustrates another method according to an embodiment of the present disclosure. As illustrated in FIG. 7, a method of using a high-carbon SPL as a fuel includes delining an electrolytic cell (1) to obtain a high-carbon SPL (122); grinding the high-carbon SPL into fuel-sized particles (124); co-feeding the high-carbon SPL and another fuel (e.g. combustible air, natural gas) into a burner (118); directing a thermal energy from the burner to a furnace (120); and scrubbing off-gases to recover fluoride compounds in operation (126).

FIG. 8 illustrates an apparatus configured to use a high-carbon SPL according to embodiments of the present invention. In one embodiment, FIG. 8 illustrates an apparatus (200) configured to use a high-carbon SPL under one or more of the aforementioned methods of using a high-carbon SPL as a fuel. As illustrated in FIG. 8, an apparatus (200) includes a solid fuel container (210); a supplemental fuel container (212); a burner system (216); a furnace (218); and a scrubber (224).

In an embodiment of the present invention, the solid fuel container (210) is configured to store and provide a solid fuel to the burner system (216). In some embodiments, the solid fuel includes a high-carbon SPL. In one embodiment, the high-carbon SPL is obtained from an electrolytic cell via delining operations (25-26). In another embodiment, the solid fuel has a carbon content of at least 65% by weight, 80% by weight, and 90% by weight. In another embodiment, the solid fuel includes a high-carbon SPL with a carbon content of at least 65% by weight, 80% by weight, and 90% by weight. In another embodiment, the solid fuel includes an enriched high-carbon SPL with a carbon content of at least 65% by weight, 80% by weight, and 90% by weight. In some embodiments, the solid fuel consists essential of high-carbon SPL. In some embodiments, the solid fuel consists essential of enriched SPL. In another embodiment, the solid fuel includes a high-carbon SPL with a carbon content of at least 75% and/or an enriched high-carbon SPL with a carbon content of at least 80% by weight.

In one embodiment of the present invention, the solid fuel produces a specific heat value when combusted in the burner (217) making it suitable for use as a fuel for a furnace (218). For example, Table 4 illustrates heat values for a high-carbon SPL fuel and for compatible enriching compounds according to embodiments of the present disclosure.

TABLE 4 Heat Value Embodiment 1 (kJ/kg) Embodiment 2 (kJ/kg) SPL Fuel Composition >18,400 >24,000 Enriching Residue >18,400 >24,000 Composition

In one embodiment, the high-carbon SPL obtained from an electrolytic cell via delining operations (25-26) has a heat value of at least 18,400 kJ/Kg. In another embodiment, the enriched SPL has a heat value of at least 18,400 kJ/Kg. In yet another embodiment, the solid fuel has a heat value of at least 18,400 kJ/Kg.

In another embodiment, the high-carbon SPL obtained from an electrolytic cell via delining operations (25-26) has a heat value of at least 24,000 kJ/Kg. In another embodiment, the enriched SPL has a heat value of at least 24,000 kJ/Kg. In yet another embodiment, the solid fuel has a heat value of at least 24,000 kJ/Kg.

In an embodiment of the present invention, the solid fuel is sized according to the requirements of the burner system (216), such as a dual-fuel combustion burner system. For example, in some embodiments, the solid fuel has an average particle size less than 150 micrometers (μm). In another embodiment, the solid fuel has an average particle size less than 90 micrometers (μm). In some embodiments, the size of the solid fuel is adjusted by sizing the high-carbon SPL or enriched SPL in the solid fuel. For example, in some embodiments, the high-carbon SPL or enriched SPL has an average particle size less than 150 micrometers (μm). In another embodiment, the high-carbon SPL or enriched SPL has an average particle size less than 90 micrometers (μm).

In some embodiments, the average particle size is obtain through physical means, such as pounding, pressing, crushing, or pulverizing the solid fuel to a desired particle size. In some embodiments, the average particle size of the high-carbon SPL is: at least about 0.1 mm; at least about 0.2 mm; at least about 0.3 mm; at least about 0.4 mm; at least about 0.5 mm; at least about 0.6 mm; at feast about 0.7 mm; at least about 0.8 mm; at least about 0.9 mm; at least about 1 mm; at least about 1.1 mm; at least about 1.2 mm; at least about 1.5 mm; at least about 1.8 mm; at least about 2 mm; at least about 2.5 mm; at least about 3 mm; at least about 3.5 mm; at least about 4 mm; at least about 4.5 mm; or at least about 5 mm. In some embodiments, the average particle size of the high-carbon SPL fuel is: not greater than about 0.1 mm; not greater than about 0.2 mm; not greater than about 0.3 mm; not greater than about 0.4 mm; not greater than about 0.5 mm; not greater than about 0.6 mm; not greater than about 0.7 mm; not greater than about 0.8 mm; not greater than about 0.9 mm; not greater than about 1 mm; not greater than about 1.1 mm; not greater than about 1.2 mm; not greater than about 1.5 mm; not greater than about 1.8 mm; not greater than about 2 mm; not greater than about 2.5 mm; not greater than about 3 mm; not greater than about 3.5 mm; not greater than about 4 mm; not greater than about 4.5 mm; or not greater than about 5 mm.

In one embodiment, about 95% of the high-carbon SPL has an average size of not greater than 0.5 mm, where substantially all (e.g. 100%) of the high-carbon SPL has an average size of not greater than 1.0 mm.

In another embodiment, the particle size of the solid fuel, the high-carbon SPL, or the enriched SPL is adjusted to improve the destruction of cyanide compounds. For example, Table 2 illustrates ranges of SPL fuel particle sizes according to one embodiment of the invention.

TABLE 2 SPL particle size <90 um <150 um (%) 95% 100%

In an embodiment of the present invention, the apparatus (200) includes a supplemental fuel container (212) configured to store and provide a supplemental fuel to the burner system (216). In some embodiments, the supplemental fuel is an oil, such as fuel oil (e.g. #2, #4, or #6), biofuel, diesel, or combinations thereof. In some embodiments, the supplemental fuel is a gas, such as natural gas (e.g. at least about 95% methane), propane, or liquefied petroleum gasses (e.g. mix of propane and butane). In other embodiments, the supplemental fuel is a combination of a fuel oil and a gas.

In an embodiment of the present invention, the apparatus (200) includes a burner system (217) configured to received and combust one or more fuels from the solid fuel container (210) or the supplemental fuel container (212).

In some embodiments, after a grinding step, a high carbon SPL is fed into solid fuel container (210) and retained until the high-carbon SPL is fed into the burner system (217) with or without feeding of a supplemental fuel to the burner system (217) from the supplemental fuel container (212).

For example, in some embodiments, high-carbon SPL from the fuel container (210) and a supplemental fuel (e.g. fuel oil or natural gas) from the supplemental fuel container (212) are directed into the burner system (216). In one embodiment, the burner system (216) is equipped with a controller, such as a programmable logic controller (PLC) injection system capable of modifying the amount of solid fuel and supplemental fuel injected into the burner system (216). In another embodiment, the burner system (216) is capable of controlling the rate that at least one of the solid fuel from the fuel container (210) and the supplemental fuel (e.g. fuel oil or natural gas) from the supplemental fuel container (212) are provided to the burner (216). In other embodiments, the burner system (217) is equipped with a mechanical injection system configured to adjust a ratio or feed rate of the solid fuel and supplemental fuel injected into the burner system (216).

In some embodiments, the burner system (217) increases the amount of solid fuel to supplemental fuel, decreases the amount of solid fuel to supplemental fuel, increases a rate of fuel injection to the burner system (217) while keeping the ratio of solid fuel the same, or decreases a rate of fuel injection to the burner system (217) while keeping the ratio of solid fuel the same.

In one embodiment of the present invention, the fuel provided to the burner system (217) includes between about 50%-80% solid fuel and about 50% and 20% supplemental fuel. In some embodiments, the solid fuel provided to the burner (217) has a carbon content of at least 65% by weight, 80% by weight, and 90% by weight. In some embodiments, the solid fuel provided to the burner (217) a heat value of at least 18,400 kJ/Kg.

In other embodiments of the present invention, the fuel provided to a burner to produce thermal energy is a combination of solid fuel and a supplemental fuel. For example, in some embodiments, the fuel provided to a burner system (217) to generate a thermal energy include a high-carbon SPL in an amount of at least about 50 wt. %; at least about 55 wt. %; at least about 60 wt. %; at least about 65 wt. %; at least about 70 wt. %; at least about 75 wt. %; at least about 80 wt. %; at least about 85 wt. %; at least about 90 wt. %; at least about 95 wt. %; or at least about 100 wt. %.

In another embodiment, the fuel provided to a burner system (217) to generate a thermal energy includes a solid fuel in an amount of at least about 50 wt. %; at least about 55 wt. %; at least about 60 wt. %; at least about 65 wt. %; at least about 70 wt. %; at least about 75 wt. %; at least about 80 wt. %; at least about 85 wt. %; at least about 90 wt. %; at least about 95 wt. %; or at least about 100 wt. %.

In another embodiment, the fuel provided to a burner system (217) to generate a thermal energy include a solid fuel with an enriched SPL in an amount of at least about 50 wt. %; at least about 55 wt. %; at least about 60 wt. %; at least about 65 wt. %; at least about 70 wt. %; at least about 75 wt. %; at least about 80 wt. %; at least about 85 wt. %; at least about 90 wt. %; at least about 95 wt. %; or at least about 100 wt. %.

In one embodiment of the present invention, a feed rate or amount of solid fuel or supplemental fuel is modified according to operation parameters of the furnace. For example, in one embodiment, at the start-up of the burner system (217), the fuel provided is mostly, if not wholly, comprises of supplemental fuel from the supplemental fuel container (212). In another embodiment, after a predetermined time, for example once a flame of combustion is established, the fuel provided to the burner system (217) is modified to increase a solid fuel/high-carbon SPL content. For example, the fuel may be modified to include at least 55 wt. %, 75 wt. %, or 80 wt % solid fuel/high-carbon SPL.

In one embodiment, the solid fuel is gravity fed to the burner (217). In another embodiment, the solid fuel is fed into the burner (217) via a carrier gas (e.g. pressurized air, at a modifiable flow rate).

In yet another embodiment, once the burner system (217) has been operating for some time, the fuel content provided to the burner system (217) is modified to reduce a content of solid fuel/high-carbon SPL to enable burner system (217) shut off and prevent any solid fuel from entering a furnace (218).

In an embodiment of the present invention, the apparatus (200) includes a furnace (218). In one embodiment, the high-carbon SPL is provided to a furnace (218) for combustion. In one embodiment, the furnace (218) is in communication with the burner system (216), and a thermal energy from the burner system (216) is supplied to the furnace (218) (e.g. directed onto/into the furnace). In one embodiment, the furnace (218) includes an enclosed combustion chamber with a combustion system power rating of at least 3 MW. For example, in one embodiment, the furnace (218) is a casthouse furnace with one or more burners forming the burner system (217).

In another example, the thermal energy is supplied to an aluminum furnace (218) to melt/assist in processing of the aluminum metal charge within the aluminum furnace (218).

In some embodiments, burners forming the burner system (217) may be directed toward the charge in the furnace (218) or angled away from the charge (e.g. such that heat is applied to the furnace walls, which then heats the charge through conduction and convection). In another embodiment, directing refers to pointing the burners forming the burner system (217) toward an external wall of the furnace (218) (e.g. sidewall and/or end), which in turn heats the furnace's walls and thus, the charge within.

In some embodiments, aluminum metal ingots (220) are processed in and produced from the aluminum furnace (218), along with associated off-gases (222) exhausted from the burner system (216) or furnace (218).

In some embodiments, the apparatus (200) includes a scrubber (224). In some embodiments, off-gasses produced by the burner system (217) or furnace (218) are scrubbed by the scrubber (224) to remove pollutants or contaminants. For example, in some embodiments, the off-gases may include fluoride compounds, which are then scrubbed by the scrubber (224). In some embodiments, the scrubber (224) cleans the off-gases 226 (removes the fluorides compounds) and/or recovers AlF₃ materials present therein. In some embodiments, the recovered AlF₃ can be reused in the electrolytic cell (1) as an electrolytic bath component.

As used herein, “scrubbing” means to the process of removing impurities or undesirable components by chemical means. In one non-limiting embodiment, scrubbing is done through a cleansing system that recovers fluoride emissions from a gaseous exhaust by contacting the gaseous exhaust with an absorptive feed (e.g. alumina).

Although a few embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined in the appended claims and their equivalents. 

What is claimed is:
 1. A method of creating a high-carbon spent pot lining (SPL) fuel, comprising: delining a spent pot lining from an electrolytic cell; and pulverizing the spent pot lining to create a spent pot lining fuel, wherein the spent pot lining comprises at least 65% by weight carbon compounds content, based on a total weight of the spent pot lining, with the remainder comprising one or more of oxygen compounds, cyanide compounds, fluoride compounds, sodium compounds, aluminum compounds, and silicon compounds.
 2. The method of claim 1, wherein the delining of the spent pot lining comprises: removing a 1^(st) bath layer; removing a metal layer; removing a 2^(nd) bath layer; cleaning a cathode block; breaking the cathode block; removing the cathode block; and removing the side blocks (27), wherein the spent pot lining consists essentially of the cathode block.
 3. The method of claim 2, further comprising: combining the spent pot lining with an enriching compound to create an enriched SPL having at least 65% carbon content, based on a total weight of the enriched SPL, wherein pulverizing the spent pot lining to create a spent pot lining fuel comprises pulverizing the enriched SPL.
 4. A method of using the SPL fuel of claim 1 as a furnace fuel, comprising: feeding a fuel comprising the SPL fuel to a burner; and combusting the fuel in the burner to generate a thermal energy and directing the thermal energy to a furnace.
 5. The method of claim 4, wherein the fuel further comprises a supplemental fuel, and wherein the SPL fuel comprises between 50% and 80% of the fuel.
 6. The method of claim 5, wherein the fuel comprises no more than 50% supplemental fuel.
 7. The method of claim 6, wherein the SPL fuel is an enriched SPL.
 8. A method of using the SPL fuel of claim 3 as a furnace fuel, comprising: feeding a fuel comprising the enriched SPL fuel to a burner; and combusting the fuel in the burner to generate a thermal energy and directing the thermal energy to a furnace.
 9. The method of claim 8, wherein the fuel further comprises a supplemental fuel, and wherein the enriched SPL fuel comprises between 50% and 80% of the fuel.
 10. The method of claim 1, wherein: the SPL fuel has a particle size of at most 150 μm, and the SPL fuel has trace amounts or less of HAP, the SPL fuel has trace amounts or less of BPC's, the SPL fuel has trace amounts or less of Dioxine, and the SPL fuel has trace amounts or less of Furan.
 11. The method of claim 10, wherein the SPL fuel comprises: at most 5% by weight oxygen compounds content, based on the total weight of the SPL fuel; at most 0.5% by weight cyanide compounds content, based on the total weight of the SPL fuel; at most 10% by weight fluoride compounds content, based on the total weight of the SPL fuel; at most 10% by weight sodium compounds content, based on the total weight of the SPL fuel; at most 5% by weight aluminum compounds content, based on the total weight of the SPL fuel; and at most 5% by weight silicon content, based on the total weight of the SPL fuel.
 12. The method of claim 11, wherein the SPL fuel has a heat value of at least 18,400 kJ/Kg.
 13. The method of claim 3, wherein the enriching compound comprises: at least 80% by weight carbon compounds content, based on a total weight of the enriching smelting residue; at most 5% by weight oxygen compounds content, based on the total weight of the enriching smelting residue; at most 0.1% by weight cyanide compounds content, based on the total weight of the enriching smelting residue; at most 5% by weight fluoride compounds content, based on the total weight of the enriching smelting residue; at most 5% by weight sodium compounds content, based on the total weight of the enriching smelting residue; at most 5% by weight aluminum compounds content, based on the total weight of the enriching smelting residue; and at most 1% by weight silicon content, based on the total weight of the enriching smelting residue.
 14. The method of claim 13, wherein the enriching compound has a heat value of at least 18,400 kJ/Kg 